Controlling exhaust gas recirculation in a turbocharged compression-ignition engine system

ABSTRACT

A method of controlling exhaust gas recirculation (EGR) in a turbocharged compression-ignition engine system including an engine, an induction subsystem in upstream communication with the engine, an exhaust subsystem in downstream communication with the engine, a high pressure EGR path between the exhaust and induction subsystems upstream of a turbocharger turbine and downstream of a turbocharger compressor, and a low pressure EGR path between the exhaust and induction subsystems downstream of the turbocharger turbine and upstream of the turbocharger compressor. A target total EGR fraction for compliance with exhaust emissions criteria is determined, then a target HP/LP EGR ratio is determined to optimize other engine system criteria within the constraints of the determined target total EGR fraction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/752,415, filed Dec. 20, 2005, and PCT Application No. 06/49084 filedDec. 20, 2006.

TECHNICAL FIELD

The field to which the disclosure generally relates includes controllingexhaust gas recirculation within turbocharged compression-ignitionengine systems.

BACKGROUND

Turbocharged engine systems include engines having combustion chambersfor combusting air and fuel for conversion into mechanical power, airinduction subsystems for conveying induction gases to the combustionchambers, and engine exhaust subsystems. The exhaust subsystemstypically carry exhaust gases away from the engine combustion chambers,muffle engine exhaust noise, and reduce exhaust gas particulates andoxides of nitrogen (NOx), which increase as engine combustiontemperatures increase. Exhaust gas is often recirculated out of theexhaust gas subsystem, into the induction subsystem for mixture withfresh air, and back to the engine. Exhaust gas recirculation increasesthe amount of inert gas and concomitantly reduces oxygen in theinduction gases, thereby reducing engine combustion temperatures and,thus, reducing NOx formation.

SUMMARY OF EXEMPLARY EMBODIMENTS OF THE INVENTION

One exemplary embodiment of a method includes controlling exhaust gasrecirculation (EGR) in a turbocharged compression-ignition enginesystem, which includes an engine, an induction subsystem in upstreamcommunication with the engine, an exhaust subsystem in downstreamcommunication with the engine, a high pressure EGR path between theexhaust and induction subsystems upstream of a turbocharger turbine anddownstream of a turbocharger compressor, and a low pressure EGR pathbetween the exhaust and induction subsystems downstream of theturbocharger turbine and upstream of the turbocharger compressor. First,a target total EGR fraction is determined for compliance with exhaustemissions criteria. Then, a target HP/LP EGR ratio is determined tooptimize other engine system criteria within the constraints of thedetermined target total EGR fraction.

According to presently preferred aspects of the exemplary embodiment ofthe method, the total EGR fraction may be estimated responsive to aproxy parameter as input to one or more engine system models, and is notdirectly measured by HP or LP EGR flow sensors or a total EGR flowsensor. Also, the target total EGR fraction may be closed-loopcontrolled by closed-loop adjustments to the HP and/or LP EGR fractions.

Other exemplary embodiments of the invention will become apparent fromthe following detailed description. It should be understood that thedetailed description and specific examples, while indicating theexemplary embodiment of the invention, are intended for purposes ofillustration only and are not intended to limit the scope of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will become more fullyunderstood from the detailed description and the accompanying drawings,wherein:

FIG. 1 is a schematic view of an exemplary embodiment of an enginesystem including an exemplary control subsystem;

FIG. 2 is a block diagram of the exemplary control subsystem of theengine system of FIG. 1;

FIG. 3 is a flow chart of an exemplary method of EGR control that may beused with the engine system of FIG. 1;

FIG. 4 is a block diagram illustrating a preferred control flow portionof the method of FIG. 3 and including a total EGR estimation block andhigh and low pressure EGR open-loop control blocks;

FIGS. 5A-5C illustrate exemplary embodiments of the estimation block ofFIG. 4;

FIGS. 6A-6B illustrate exemplary embodiments of the high and lowpressure EGR open-loop control blocks of FIG. 4;

FIG. 7 is a graph illustrating an exemplary plot of valve positionversus target total EGR fraction;

FIG. 8 is a block diagram illustrating a second control flow portion ofthe method of FIG. 3;

FIG. 9 a block diagram illustrating a third control flow portion of themethod of FIG. 3; and

FIG. 10 is a block diagram illustrating a fourth control flow portion ofthe method of FIG. 3.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description of the embodiment(s) is merely exemplary innature and is in no way intended to limit the invention, itsapplication, or uses.

According to an exemplary embodiment of a method, exhaust gasrecirculation (EGR) is controlled in a turbocharged compression-ignitionengine system having high pressure (HP) and low pressure (LP) EGR paths.Preferably, total EGR fraction is estimated responsive to a proxyparameter as input to one or more engine system models, and is notdirectly measured by HP or LP EGR flow sensors or a total EGR flowsensor. A target total EGR fraction is determined for compliance withexhaust emissions criteria. Then, a target HP/LP EGR ratio is determinedfor optimization of other criteria, such as at least one of fuel economytargets, engine system performance goals, or engine system protection ormaintenance specifications, within the constraints of the determinedtarget total EGR fraction. Also preferably, the target total EGRfraction is closed-loop controlled by closed-loop adjustments to the HPand/or LP EGR fractions. Set forth below, an exemplary system isdescribed for carrying out the method, and an exemplary method andexemplary control flows are also described.

Exemplary System

An exemplary operating environment is illustrated in FIG. 1, and may beused to implement a presently disclosed method of EGR control. Themethod may be carried out using any suitable system and, preferably, iscarried out in conjunction with an engine system such as system 10. Thefollowing system description simply provides a brief overview of oneexemplary engine system, but other systems and components not shown herecould also support the presently disclosed method.

In general, the system 10 may include an internal combustion engine 12to develop mechanical power from internal combustion of a mixture offuel and induction gases, an induction subsystem 14 to generally providethe induction gases to the engine 12 and, an exhaust subsystem 16 toconvey combustion gases generally away from the engine 12. As usedherein, the phrase induction gases may include fresh air andrecirculated exhaust gases. The system 10 also generally may include aturbocharger 18 in communication across the exhaust and inductionsubsystems 14, 16 to compress inlet air to improve combustion andthereby increase engine output. The system 10 further generally mayinclude an exhaust gas recirculation subsystem 20 across the exhaust andinduction subsystems 14, 16 to recirculate exhaust gases for mixturewith fresh air to improve emissions performance of the engine system 10.The system 10 further generally may include a control subsystem 22 tocontrol operation of the engine system 10. Those skilled in the art willrecognize that a fuel subsystem (not shown) is used to provide anysuitable liquid and/or gaseous fuel to the engine 12 for combustiontherein with the induction gases.

The internal combustion engine 12 may be any suitable type of engine,such as an autoignition or compression-ignition engine like a dieselengine. The engine 12 may include a block 24 with cylinders and pistonstherein (not separately shown), which along with a cylinder head (alsonot separately shown), define combustion chambers (not shown) forinternal combustion of a mixture of fuel and induction gases.

The induction subsystem 14 may include, in addition to suitable conduitand connectors, an inlet end 26 which may have an air filter (not shown)to filter incoming air, and a turbocharger compressor 28 downstream ofthe inlet end 26 to compress the inlet air. The induction subsystem 14may also include a charge air cooler 30 downstream of the turbochargercompressor 28 to cool the compressed air, and an intake throttle valve32 downstream of the charge air cooler 30 to throttle the flow of thecooled air to the engine 12. The induction subsystem 14 also may includean intake manifold 34 downstream of the throttle valve 32 and upstreamof the engine 12, to receive the throttled air and distribute it to theengine combustion chambers.

The exhaust subsystem 16 may include, in addition to suitable conduitand connectors, an exhaust manifold 36 to collect exhaust gases from thecombustion chambers of the engine 12 and convey them downstream to therest of the exhaust subsystem 16. The exhaust subsystem 16 also mayinclude a turbocharger turbine 38 in downstream communication with theexhaust manifold 36. The turbocharger 18 may be a variable turbinegeometry (VTG) type of turbocharger, a dual stage turbocharger, or aturbocharger with a wastegate or bypass device, or the like. In anycase, the turbocharger 18 and/or any turbocharger accessory device(s)may be adjusted to affect any one or more of the following parameters:turbocharger boost pressure, air mass flow, and/or EGR flow. The exhaustsubsystem 16 may also include any suitable emissions device(s) 40 suchas a catalytic converter like a close-coupled diesel oxidation catalyst(DOC) device, a nitrogen oxide (NOx) adsorber unit, a particulatefilter, or the like. The exhaust subsystem 16 may also include anexhaust throttle valve 42 disposed upstream of an exhaust outlet 44.

The EGR subsystem 20 is preferably a hybrid or dual path EGR subsystemto recirculate portions of the exhaust gases from the exhaust subsystem16 to the induction subsystem 14 for combustion in the engine 12.Accordingly, the EGR subsystem 20 may include two paths: a high pressure(HP) EGR path 46 and a low pressure (LP) EGR path 48. Preferably, the HPEGR path 46 is connected to the exhaust subsystem 16 upstream of theturbocharger turbine 38 but connected to the induction subsystem 12downstream of the turbocharger compressor 28. Also preferably, the LPEGR path 48 is connected to the exhaust subsystem 16 downstream of theturbocharger turbine 38 but connected to the induction subsystem 14upstream of the turbocharger compressor 28. Any other suitableconnection between the exhaust and induction sub-systems 14, 16 is alsocontemplated including other forms of HP EGR such as the usage ofinternal engine variable valve timing and lift to induce internal HPEGR.

The HP EGR path 46 may include, in addition to suitable conduit andconnectors, an HP EGR valve 50 to control recirculation of exhaust gasesfrom the exhaust subsystem 16 to the induction subsystem 14. The HP EGRvalve 50 may be a stand-alone device having its own actuator or may beintegrated with the intake throttle valve 32 into a combined devicehaving a common actuator. The HP EGR path 46 may also include an HP EGRcooler 52 upstream, or optionally downstream, of the HP EGR valve 50 tocool the HP EGR gases. The HP EGR path 46 is preferably connectedupstream of the turbocharger turbine 38 and downstream of the throttlevalve 32 to mix HP EGR gases with throttled air and other inductiongases (the air may have LP EGR).

The LP EGR path 48 may include, in addition to suitable conduit andconnectors, an LP EGR valve 54 to control recirculation of exhaust gasesfrom the exhaust subsystem 16 to the induction subsystem 14. The LP EGRvalve 54 may be a stand-alone device having its own actuator or may beintegrated with the exhaust throttle valve 42 into a combined devicehaving a common actuator. The LP EGR path 48 may also include an LP EGRcooler 56 downstream, or optionally upstream, of the LP EGR valve 54 tocool the LP EGR gases. The LP EGR path 48 is preferably connecteddownstream of the turbocharger turbine 38 and upstream of theturbocharger compressor 28 to mix LP EGR gases with filtered inlet air.

Referring now to FIG. 2, the control subsystem 22 may include anysuitable hardware, software, and/or firmware to carry out at least someportions of the methods disclosed herein. For example, the controlsubsystem 22 may include some or all of the engine system actuators 58discussed above, as well as various engine sensors 60. The engine systemsensors 60 are not individually shown in the drawings but may includeany suitable devices to monitor engine system parameters.

For example, an engine speed sensor measures the rotational speed of anengine crankshaft (not shown), pressure sensors in communication withthe engine combustion chambers measure engine cylinder pressure, intakeand exhaust manifold pressure sensors measure pressure of gases flowinginto and away from the engine cylinders, an inlet air mass flow sensormeasures incoming airflow in the induction subsystem 14, and a manifoldmass flow sensor measures flow of induction gases to the engine 12. Inanother example, the engine system 10 may include a temperature sensorto measure the temperature of induction gases flowing to the enginecylinders, and a temperature sensor downstream of the air filter andupstream of the turbocharger compressor 28. In a further example, theengine system 10 may include a speed sensor suitably coupled to theturbocharger compressor 28 to measure the rotational speed thereof. Athrottle position sensor, such as an integrated angular position sensor,measures the position of the throttle valve 32. A position sensor isdisposed in proximity to the turbocharger 18 to measure the position ofthe variable geometry turbine 38. A tailpipe temperature sensor may beplaced just upstream of a tailpipe outlet to measure the temperature ofthe exhaust gases exiting the exhaust subsystem 16. Also, temperaturesensors are placed upstream and downstream of the emissions device(s) 40to measure the temperature of exhaust gases at the inlet(s) andoutlet(s) thereof. Similarly, one or more pressure sensors are placedacross the emissions device(s) 40 to measure the pressure dropthereacross. An oxygen (O₂) sensor is placed in the exhaust and/orinduction subsystems 14, 16, to measure oxygen in the exhaust gasesand/or induction gases. Finally, position sensors measure the positionsof the HP and LP EGR valves 50, 54 and the exhaust throttle valve 42.

In addition to the sensors 60 discussed herein, any other suitablesensors and their associated parameters may be encompassed by thepresently disclosed system and methods. For example, the sensors 60could also include accelerator sensors, vehicle speed sensors,powertrain speed sensors, filter sensors, other flow sensors, vibrationsensors, knock sensors, intake and exhaust pressure sensors, and/or thelike. In other words, any sensors may be used to sense any suitablephysical parameters including electrical, mechanical, and chemicalparameters. As used herein, the term sensor includes any suitablehardware and/or software used to sense any engine system parameterand/or various combinations of such parameters.

The control subsystem 22 may further include one or more controllers(not shown) in communication with the actuators 58 and sensors 60 forreceiving and processing sensor input and transmitting actuator outputsignals. The controller(s) may include one or more suitable processorsand memory devices (not shown). The memory may be configured to providestorage of data and instructions that provides at least some of thefunctionality of the engine system 10 and that may be executed by theprocessor(s). At least portions of the method may be enabled by one ormore computer programs and various engine system data or instructionsstored in memory as look-up tables, maps, models, or the like. In anycase, the control subsystem 22 controls engine system parameters byreceiving input signals from the sensors 60, executing instructions oralgorithms in light of sensor input signals, and transmitting suitableoutput signals to the various actuators 58.

The control subsystem 22 may include several modules in thecontroller(s). For example, a top level engine control module 62receives and processes any suitable engine system input signals andcommunicates output signals to an induction control module 64, a fuelcontrol module 66, and any other suitable control modules 68. As will bediscussed in greater detail below, the top level engine control module62 receives and processes input signals from one or more of the enginesystem parameter sensors 60 to estimate total EGR fraction in anysuitable manner.

Various methods of estimating EGR fraction are known to those skilled inthe art. As used herein, the phrase “total EGR fraction” includes one ormore of its constituent parameters, and may be represented by thefollowing equation:

$r_{EGR} = {{\left( {1 - \frac{M\; A\; F}{M_{ENG}}} \right)*100} = {\left( \frac{M_{EGR}}{M_{ENG}} \right)*100\mspace{14mu}{where}}}$

-   -   MAF is fresh air mass flow into an induction subsystem,    -   M_(EGR) is EGR mass flow into the induction subsystem,    -   M_(ENG) is induction gas mass flow to an engine, and    -   r_(EGR) includes that portion of induction gases entering an        engine attributable to recirculated exhaust gases.

From the above equation, the total EGR fraction may be calculated usingthe fresh air mass flow sensor and induction gas mass flow from a sensoror from an estimate thereof, or using an estimate of total EGR fractionitself and the induction gas mass flow. In either case, the top levelengine control module 62 may include suitable data inputs to estimatethe total EGR fraction directly from one or more mass flow sensormeasurements or estimations as input to one or more engine systemmodels.

As used herein, the term “model” includes any construct that representssomething using variables, such as a look up table, map, algorithmsand/or the like. Models are application specific and particular to theexact design and performance specifications of any given engine system.In one example, the engine system models in turn may be based on enginespeed and intake manifold pressure and temperature. The engine systemmodels are updated each time engine parameters change, and may bemulti-dimensional look up tables using inputs including engine speed andengine intake density, which may be determined with the intake pressure,temperature, and universal gas constant.

The total EGR fraction may be correlated, directly or indirectly via itsconstituents, to one or more engine system parameters, such as estimatedor sensed air mass flow, O₂, or engine system temperature(s). Suchparameters may be analyzed in any suitable fashion for correlation withthe total EGR fraction. For example, the total EGR fraction may beformulaically related to the other engine system parameters. In anotherexample, from engine calibration or modeling, the total EGR fraction maybe empirically and statistically related to the other engine systemparameters. In any case, where the total EGR fraction is found toreliably correlate to any other engine system parameter(s), thatcorrelation may be modeled formulaically, empirically, acoustically,and/or the like. For example, empirical models may be developed fromsuitable testing and may include lookup tables, maps, and the like thatmay cross reference total EGR fraction values with other engine systemparameter values.

Accordingly, an engine system parameter may be used as a proxy fordirect sensor measurements of total EGR fraction and/or individual HPand/or LP EGR flow. Accordingly, total EGR, HP EGR, and LP EGR flowsensors may be eliminated, thereby saving on engine system cost andweight. Elimination of such sensors also leads to elimination of othersensor-related hardware, software, and costs, such as wiring, connectorpins, computer processing power and memory, and so on.

Also, the top level engine control 62 module preferably calculates aturbocharger boost pressure setpoint and a target total EGR setpoint,and transmits these setpoints to the induction control module 64.Similarly, the top level engine control module 62 calculates suitabletiming and fueling setpoints and transmits them to the fuel controlmodule 66, and calculates other setpoints and transmits them to theother control modules 68. The fuel and other control modules 66, 68receive and process such inputs, and generate suitable command signalsto any suitable engine system devices such as fuel injectors, fuelpumps, or other devices.

Alternatively, the top level engine control module 62 may calculate andtransmit the boost pressure setpoint and a total intake air mass flowsetpoint (as shown in dashed lines), instead of the target total EGRsetpoint. In this alternative case, the total EGR setpoint issubsequently determined from the air mass flow setpoint in much the sameway the actual total EGR fraction is estimated from the actual mass flowsensor readings. In a second alternative, air mass flow replaces totalEGR fraction throughout the control method. This changes the types ofdata used and the manner in which HP and LP EGR flow targets are set,but the basic structure of the controller and flow of the control methodis the same.

The induction control module 64 receives any suitable engine systemparameter values, in addition to the setpoints received from the toplevel engine control module 62. For example, the induction controlmodule 64 receives induction and/or exhaust subsystem parameter valueslike turbocharger boost pressure, and mass flow. The induction controlmodule 64 may include a top level induction control submodule 70 thatprocesses the received parameter values, and transmits any suitableoutputs such as LP and HP EGR setpoints, and turbocharger setpoints torespective LP EGR, HP EGR, and turbocharger control submodules 72, 74,76. The LP EGR, HP EGR, and turbocharger control submodules 72, 74, 76process such induction control submodule outputs and generate suitablecommand signals to various engine system devices such as the LP EGRvalve 54 and exhaust throttle valve 42, HP EGR valve 50 and intakethrottle valve 32, and one or more turbocharger actuators 19. Thevarious modules and/or submodules may be separate as shown, or may beintegrated into one or more combined modules and/or submodules.

Exemplary Method(s)

A method of controlling LP and HP EGR is provided herein and may becarried out as one or more computer programs within the operatingenvironment of the engine system 10 described above. Those skilled inthe art will also recognize that the method may be carried out usingother engine systems within other operating environments. Referring nowto FIG. 3, an exemplary method 300 is illustrated in flow chart form.

As shown at step 305, the method 300 may be initiated in any suitablemanner. For example, the method 300 may be initiated at startup of theengine 12 of the engine system 10 of FIG. 1.

At step 310, fresh air is drawn into an induction subsystem of an enginesystem, and induction gases are inducted into an engine of the enginesystem through the induction subsystem. For example, fresh air may bedrawn into the inlet 26 of the induction system 14, and induction gasesmay be inducted into the engine 12 through the intake manifold 34.

At step 315, exhaust gases are exhausted from an engine through anexhaust subsystem of an engine system. For example, exhaust gases may beexhausted from the engine 12 through the exhaust manifold 36.

At step 320, exhaust gases are recirculated from an exhaust subsystemthrough one or both of high or low pressure EGR paths to an inductionsubsystem of an engine system. For example, HP and LP exhaust gases maybe recirculated from the exhaust subsystem 16, through the HP and LP EGRpaths 46, 48, to the induction subsystem 14.

At step 325, one or more proxy parameters may be sensed that is/areindicative of total EGR fraction. For example, the proxy parameter(s)may include air mass flow, O₂, and/or engine system temperatures, andmay be measured by respective sensors 60 of the engine system 10.

At step 330, a target total EGR fraction is determined for compliancewith exhaust emissions criteria. For example, the top level enginecontrol module 62 may use any suitable engine system model(s) tocross-reference current engine operating parameters with desirable totalEGR fraction values to comply with predetermined emissions standards. Asused herein, the term “target” includes a single value, multiple values,and/or any range of values. Also, as used herein, the term “criteria”includes the singular and the plural. Examples of criteria used todetermine appropriate EGR fraction(s) include calibrated tables based onspeed and load, model based approaches which determine cylindertemperatures targets and convert to EGR fraction and operatingconditions such as transient operation or steady state operation.Absolute emissions criteria may be dictated by environmental entitiessuch as the U.S. Environmental Protection Agency (EPA).

At step 335, a target HP/LP EGR ratio is determined to optimize one ormore other engine system criteria such as fuel economy goals, enginesystem performance goals, or engine system protection or maintenancespecifications, and as constrained by the target total EGR fractiondetermined in step 330.

At step 340, individual HP EGR and/or LP EGR setpoints may be generatedin accordance with the target HP/LP EGR ratio determined in step 335.

At step 345, target HP and LP EGR opening percentages corresponding tothe HP and LP EGR setpoints may be determined. For example, open-loopcontrollers may process the HP and LP EGR setpoints and other enginesystem parameters using models to generate the opening percentages.

At step 350, total EGR fraction may be estimated responsive to the proxyparameter(s), which are used as input to any suitable engine systemmodels as discussed previously above. For example, the total EGRfraction estimate may include engine system models to formulaically orempirically correlate the proxy parameter(s) to the total EGR fraction.The models may include lookup tables, maps, and the like, that may crossreference EGR fraction values with proxy parameter values, and may bebased on engine speed and intake manifold pressure and temperature. Inany case, the total EGR fraction is not actually directly measured usingindividual HP and/or LP EGR flow sensors or a combined total EGR flowsensor.

At step 355, one or both of the individual HP EGR and/or LP EGRfractions may be adjusted using closed-loop control with the estimatedtotal EGR fraction. The HP and/or LP EGR fractions may be adjusted viaclosed-loop control of either or both of the respective HP and/or LP EGRsetpoints or the valve and/or throttle opening percentages. For example,and as will be discussed in greater detail below, a closed-loopcontroller may process the estimated total EGR fraction as processvariable input and the total EGR fraction setpoint as a setpoint input,in order to generate an HP and/or LP EGR setpoint output trim command.Thus, the target total EGR fraction preferably is closed-loop controlledby closed-loop adjustments to the HP and/or LP EGR fractions. Suchadjustments may change the actual HP/LP EGR ratio.

At step 360, the HP EGR and LP EGR opening percentages from step 350 maybe applied to one or more respective HP EGR, LP EGR, intake throttle, orexhaust throttle valves. The HP and/or LP EGR opening percentages areadjusted directly, downstream of the open-loop control blocks orindirectly via setpoint adjustment upstream of the open-loop controlblocks.

Exemplary Control Flows

Referring now to the controls diagram of FIG. 4, a portion of thecontrol method 300 from FIG. 3 is illustrated in block form as an EGRcontrol flow 400. The control flow 400 may be carried out, for example,within the exemplary control subsystem of FIG. 2 and, more particularly,within the induction control module 64 thereof. Accordingly, FIG. 4illustrates the HP and LP EGR control submodules or blocks 72, 74 andthe turbocharger boost control submodule or block 76. Similarly, anoptimization block 402, an EGR fraction estimator block 404, and an EGRfraction closed-loop control block 406 may also be carried out withinthe induction control module 64 and, more particularly, within the toplevel induction control submodule 70 of FIG. 2.

First, and referring also to FIGS. 5A-5C, the actual total EGR fractionestimator block 404 is preferably carried out using the proxyparameter(s) for the actual total EGR fraction in addition to otherstandard engine system parameters such as engine load, engine speed,turbocharger boost pressure, and engine system temperatures. Forexample, FIG. 5A illustrates that the preferred proxy parameter is airmass flow 414 a, which may be obtained from any suitable air mass flowestimate or reading such as from the intake air mass flow sensor. Inanother example, FIG. 5B illustrates that the proxy parameter may beoxygen percentage 414 b, such as from an O₂ sensor like the O₂ sensordisposed in the induction subsystem 14. For instance, the O₂ sensor maybe a universal exhaust gas oxygen sensor (UEGO), which may be located inthe intake manifold 34. In a further example, FIG. 5C illustrates thatthe proxy parameter may be induction subsystem and exhaust subsystemtemperature 414 c taken from temperature sensors. For instance, inletair temperature may be used such as from the air inlet temperaturesensor, exhaust temperature such as from the exhaust temperature sensor,and manifold temperature such as from the intake manifold temperaturesensor. In all of the above-approaches, the actual total EGR fraction416 may be estimated from one or more proxy parameter types.

Second, and referring again to FIG. 4, the optimization block 402receives and processes various engine system inputs to identify anoptimal HP/LP EGR ratio and generate an HP EGR setpoint according tothat ratio. For example, the optimization block 402 may receive theengine load signal 407 and the engine speed signal 408, such as fromcorresponding sensors in the engine system 10. The engine load signal407 may include any parameters such as manifold pressure, fuel injectionflow, etc. The optimization block 402 may also receive a total EGRfraction setpoint 418 such as from the top level engine control module62.

The optimization block 402 may prioritize fuel economy criteria foridentifying the optimal HP/LP EGR ratio and generating the correspondingHP EGR setpoint. According to fuel economy optimization, theoptimization block 402 may include any suitable net turbochargerefficiency model that encompasses various parameters such as pumpinglosses, and turbine and compressor efficiencies. The efficiency modelmay include a principles based mathematical representation of the engineinduction subsystem 14, a set of engine system calibration tables, orthe like. Example criteria used to determine desired EGR ratios to meetfuel economy criteria may include setting a ratio that allows the totalEGR fraction to be achieved without the need for closing the intake orexhaust throttles, which closing tends to negatively impact fueleconomy, or the ratio may be adjusted to achieve an optimal inductionair temperature for maximum fuel economy.

The optimization block 402 may also override the fuel economy criteriato instead optimize other engine system criteria for any suitablepurpose. For example, the fuel economy criteria may be overridden toprovide an HP/LP EGR ratio that provides improved engine systemperformance, such as increased torque output in response to driverdemand for vehicle acceleration. In this case, the controller may favora higher percentage of LP EGR which allows better turbocharger speed-upto reduce turbo lag. In another example, the override may provide adifferent HP/LP EGR ratio to protect the engine system 10 such as toavoid a turbocharger overspeed condition or excess compressor tiptemperatures, or to reduce turbocharger condensate formation, or thelike. In a further example, the override may provide another HP/LP EGRratio to maintain the engine system 10 such as by affecting induction orexhaust subsystem temperatures. For instance, exhaust subsystemtemperatures may be increased to regenerate a diesel particulate filter,and induction temperatures may be reduced to cool the engine 12. As afurther example, induction air temperature may be controlled to reducethe potential for water condensate to form in the inlet induction path.

In any case, the optimization block 402 processes the inputs inaccordance with its model(s) to determine the target HP/LP EGR ratio andthen generate an HP EGR setpoint 420, which is fed downstream to the HPEGR control block 74 and to an arithmetic node 422, which also receivesthe total EGR fraction setpoint 418 from the top level engine controlmodule 62 to yield an LP EGR setpoint 424.

Third, and still referring to FIG. 4, the total EGR fraction closed-loopcontrol block 406 may be any suitable closed-loop control means, such asa PID controller block or the like, for controlling the total EGRfraction. The closed-loop control block 406 includes a setpoint input406 a to receive the target total EGR fraction setpoint from the toplevel engine control module 62 and further may include a processvariable input 406 b to receive the actual total EGR fraction estimatefrom the estimator block 404. The total EGR fraction control block 406processes these inputs to generate a feedback control signal or trimcommand 406 c for summation at another arithmetic node 426 with the LPEGR setpoint 424 for input downstream at the LP EGR control block 72.Such trim adjustment may also or instead be calculated as an adjustmentto the LP EGR valve and/or exhaust throttle valve percentage openingcommand(s) and added after the LP EGR open-loop control block 72.Accordingly, the control block 406 and associate nodes would becommunicated to the open-loop control block 72 at a downstream sidethereof to adjust suitable setpoints for the valve and throttle openingpercentages.

Because the HP EGR flow is only open-loop controlled, the LP EGR flow orfraction is adjusted by the closed-loop control block 406 to achieve thetarget total EGR fraction. More specifically, because exhaust emissionsand engine fuel economy are both highly dependent on total EGR fractionand to a lesser extent on the HP/LP EGR ratio, the total EGR fraction isclosed-loop controlled for maximum control whereas the HP and/or LP EGRfractions and/or the HP/LP EGR ratio is/are at least partially open-loopcontrolled for maximum cost-effectiveness and efficiency. Theseopen-loop control blocks 72, 74 provide good response time, reducecontroller interdependencies, and reduce the effects of transients anddisturbances in sensor signals. While this is one exemplary approach,other approaches are discussed below in reference to FIGS. 8-10.

Fourth, the LP and HP EGR control blocks 72, 74 receive their respectiveLP and HP EGR setpoints in addition to the turbocharger boost pressure409 and the engine load and speed inputs 407, 408. The LP and HP EGRcontrol blocks 72, 74 receive such inputs for open-loop or feedforwardcontrol of their respective LP and HP EGR actuators. For instance, theLP and HP EGR control blocks 72, 74 output LP EGR valve and/or exhaustthrottle commands 430, 432, and HP EGR valve and/or intake throttlecommands 438, 440. The LP and HP EGR control blocks 72, 74 may correlateHP and LP EGR flow to suitable HP and LP EGR valve and/or throttlepositions using one or more models.

As shown in FIGS. 6A and 6B, the LP and HP EGR control blocks 72, 74 mayinclude various open-loop control models. For instance, the LP EGRcontrol block 72 may include any suitable model(s) 426 to correlate theLP EGR setpoint 424 to the LP EGR valve position to help achieve thetarget HP/LP EGR ratio. Also, the LP EGR control block 72 may includeany suitable model(s) 428 to correlate the LP EGR setpoint 424 to theexhaust throttle position to help achieve the target HP/LP EGR ratio.The models 426, 428 may receive any suitable inputs such as the engineload 407, the engine speed 408, and the turbocharger boost pressure 409.The models 426, 428 are executed to generate, respectively, the LP EGRvalve command 430 and/or the exhaust throttle command 432 for use byrespective actuators. Note that the actuators may operate in an openloop mode, or may be operatively coupled with any suitable sensors tomeasure actuator position and adjust the commands to achieve the targetpercentages.

Likewise, the HP EGR control block 74 may include any suitable model(s)434 to correlate the HP EGR setpoint 420 to the HP EGR valve position tohelp achieve the target HP/LP EGR ratio. Also, the HP EGR control block74 may include any suitable model(s) 436 to correlate the HP EGRsetpoint 420 to the intake throttle position to help achieve the targetHP/LP EGR ratio. Again, the models 434, 436 may receive any suitableinputs such as the engine load 407, the engine speed 408, and theturbocharger boost pressure 409. The models 434, 436 are executed togenerate, respectively, an HP EGR valve command 438 and/or an intakethrottle command 440 for use by respective actuators.

FIG. 7 illustrates a graph of exemplary LP EGR valve and exhaustthrottle opening percentages vs. target total EGR fraction. As shown,the throttle valve 42 may be substantially closed at about 0% EGR andgradually opens to a substantially 100% open position at about 20% EGR,whereas the LP EGR valve 54 stays substantially closed from about 0% EGRto about 20% EGR. Thereafter, the exhaust throttle 42 stays 100% openuntil the total EGR reaches about 70%, and the LP EGR valve 54 graduallyopens to substantially 100% open at about 70% EGR. Thereafter, the LPEGR valve 54 remains substantially 100% open, while the exhaust throttlevalve 42 gradually closes until it is substantially closed at 100% EGR.A single, combined, LP EGR and exhaust throttle valve could be usedinstead of two separate valves as long as such a unitary valve devicecould substantially achieve the valve openings just described.

Referring again to FIG. 4, the turbocharger boost control block 76 isany suitable closed-loop control means, such as suitable PID controlblock, for adjusting turbocharger actuators to achieve a target boostpressure within safe turbo operating boundaries. The control block 76may include a setpoint input 76 a to receive boost setpoint from the toplevel engine control module 62, and an actual boost pressure input 76 bfrom the turbocharger boost sensor. The control block 76 processes theseinputs and generates any suitable turbocharger command output such as avariable turbine geometry command 444 to adjust variable vanes of theturbocharger 18.

Referring now to FIG. 8, an alternative control flow 800 may be used inplace of the preferred control flow 400. This embodiment is similar inmany respects to the embodiment of FIG. 4, and like numerals between theembodiments generally designate like or corresponding elementsthroughout the several views of the drawing figures. Additionally, thedescription of the previous embodiment is incorporated by reference andthe common subject matter may generally not be repeated here.

The alternative control flow 800 involves closed-loop adjustment of HPEGR instead of LP EGR. In other words, an HP EGR setpoint 420′—insteadof an LP EGR setpoint 424′—may be adjusted to control the total EGRfraction. Accordingly, the closed-loop control block 406 may generate acontrol signal to adjust the HP EGR fraction—instead of the LP EGRfraction. To accommodate this change in control strategy, anoptimization block 402′ may be provided to output an LP EGR setpoint424′ instead of the HP EGR setpoint 420. Such trim adjustment may alsoor instead be calculated as an adjustment to the HP EGR valve and/orintake throttle valve percentage opening command(s) and added after theHP EGR open-loop control block 74. Accordingly, the control block 406and associate nodes would be communicated to the open-loop control block74 at a downstream side thereof to adjust suitable setpoints for thevalve and throttle opening percentages. Otherwise, the flow 800 issubstantially similar to flow 400.

Referring now to FIG. 9, a second control flow 900 may be used in placeof the preferred control flow 400. This embodiment is similar in manyrespects to the embodiment of FIG. 4, and like numerals between theembodiments generally designate like or corresponding elementsthroughout the several views of the drawing figures. Additionally, thedescription of the previous embodiment is incorporated by reference andthe common subject matter may generally not be repeated here.

In the second control flow 900, closed-loop control may be allocated toHP and LP EGR fractions in the same proportion as the HP and LP EGRsetpoints. In other words, HP and LP EGR fractions are both closed-loopadjusted in proportion to their respective HP and LP EGR setpoints.

To facilitate this change in control strategy, the closed-loop controlblock 406 does not output its trim command 406 c only to the LP EGRcontrol block 72 via the upstream arithmetic node 426 as in flow 400.Rather, the trim command is output to both the LP and HP EGR controlblocks 72, 74. To further facilitate this change, proportionalarithmetic blocks 950, 952 receive respective HP and LP EGR setpointsand the total EGR setpoint 418. The proportional output from thearithmetic blocks 950, 952 is received at multiplication arithmeticblocks 954, 956 for proportional allocation of the closed-loop trimcommand 406 c thereto. The multiplication outputs are summed atdownstream arithmetic nodes 426, 926 with the LP and HP EGR setpointsfor input downstream at the LP and HP EGR control blocks 72, 74.Suitable checks could be implemented within the arithmetic blocks toavoid dividing by 0 when the total EGR fraction set-point is 0.Otherwise the flow 900 is substantially similar to that in flows 400and/or 800.

Referring now to FIG. 10, a third exemplary control flow 1000 may beused in place of the preferred control flow 400. This embodiment issimilar in many respects to the embodiment of FIG. 4, and like numeralsbetween the embodiments generally designate like or correspondingelements throughout the several views of the drawing figures.Additionally, the description of the previous embodiment is incorporatedby reference and the common subject matter may generally not be repeatedhere.

In the third control flow 1000, closed-loop control may be switched backand forth between the LP and HP EGR open-loop control blocks 72, 74depending on engine operating conditions at any given moment. In otherwords, either HP or LP EGR setpoints may be adjusted with closed-loopcontrol. For example, HP EGR may be closed-loop controlled to avoidturbocharger condensation when engine system temperatures are relativelyhigh, or when a rapid change in total EGR fraction is required, or whenthe turbocharger performance is less important or not required.

To accomplish the change in control strategy, a closed-loop controlblock 1006 does not provide output only to the LP EGR control block 72via the upstream arithmetic node 426 as in flow 400. Rather, the controlblock 1006 provides output to both the LP and HP EGR control blocks 72,74. The closed-loop control block 1006 may include a setpoint input 1006a to receive the target total EGR fraction setpoint 418 from the toplevel engine control module 62 and further may include a processvariable input 1006 b to receive the actual total EGR fraction estimatefrom the estimator block 404. The total EGR fraction control block 1006processes these inputs to generate alternative trim commands; an LP EGRtrim command 1006 c for summation at arithmetic node 426 with the LP EGRsetpoint 424 for input downstream at the LP EGR control block 72, and anHP EGR trim command 1006 d for summation at another arithmetic node 1026with the HP EGR setpoint 420 for input downstream at the HP EGR controlblock 74. The control block 1006 may be switched between the two outputs1000 c, 1000 d such that the LP EGR fraction or the HP EGR fraction maybe adjusted by the closed-loop control block 1006 to achieve the targettotal EGR fraction. Otherwise, the flow 1000 is substantially similar tothat in flows 400 and/or 800.

One or more of the various illustrative embodiments above may includeone or more of the following advantages. First, a total target EGRfraction may be allocated to HP and LP EGR paths in a manner to firstcomply with emissions regulations, and then to optimize engine fueleconomy and performance and protect and maintain an engine system.Second, use of individual total EGR, HP EGR, or LP EGR flow sensors isnot required, which sensors are costly, complicate an engine system, andintroduce failure modes. Third, one standard closed-loop control meansmay be used to control a target total EGR fraction as well as theindividual HP and LP EGR flows, thereby allowing practical andcost-effective implementation in current engine control architectures.Fourth, a combined LP EGR valve and exhaust throttle valve controlled bya single common actuator may be used and, likewise, a combined HP EGRvalve and intake throttle valve controlled by a single common actuatormay also be used.

The above description of embodiments of the invention is merelyexemplary in nature and, thus, variations thereof are not to be regardedas a departure from the spirit and scope of the invention.

What is claimed is:
 1. A product comprising: a control subsystemconfigured to: utilize at least one mass flow sensor to measured themass flow of at least one gas in an induction plenum of an engine; usethe measured mass flow as input to one or more system models; estimate atarget total EGR fraction responsive to the one or more engine systemmodels, and at least one other engine system input signal; send a signalrepresentative of the target total EGR fraction to a controllerconfigured to control exhaust gas recirculation (EGR) wherein thecontroller is also configured to: receive input signals including thetarget total EGR fraction of an EGR system comprising at least two EGRpaths, determine a target HP/LP EGR ratio to control other engine systemparameters within the constraints of the target total EGR fraction, andtransmit actuator output signals responsive to the target HP/LP EGRratio; wherein the controller is further configured to: generate HP EGRand LP EGR setpoints in accordance with the determined target HP/LP EGRratio, determine target HP and LP EGR valve opening percentagescorresponding to the HP and LP EGR setpoints, adjust at least one of thesetpoints or opening percentages by processing an estimated total EGRfraction as process variable input and the target total EGR fraction assetpoint input, and transmit the opening percentages as the actuatoroutput signals to an EGR valve actuator configured to move an EGR valvein response to the actuator output signal.
 2. A product as set forth inclaim 1 wherein the other engine system parameters include at least oneof fuel economy, engine system performance, engine system protection, orengine system maintenance.
 3. A product as set forth in claim 2 whereinthe other engine system parameters include at least one of inductionsubsystem temperature control or exhaust subsystem temperature control.4. A product as set forth in claim 3 wherein the target HP/LP EGR ratiois determined to increase exhaust subsystem temperatures to regenerate adiesel particulate filter.
 5. A product as set forth in claim 3 whereinthe target HP/LP EGR ratio is determined to reduce induction subsystemtemperatures.
 6. A product as set forth in claim 3 wherein the targetHP/LP EGR ratio is determined to control induction air temperature toavoid condensation.
 7. A product as set forth in claim 2 wherein thetarget HP/LP EGR ratio is determined to avoid turbocharger overspeeding.8. A product as set forth in claim 2 wherein the target HP/LP EGR ratiois determined to increase torque output in response to driver demand forvehicle acceleration.
 9. A product as set forth in claim 2 wherein thetarget HP/LP EGR ratio is determined to provide a higher percentage ofLP EGR to reduce turbocharger lag.
 10. A product as set forth in claim 2wherein the target HP/LP EGR ratio is determined to allow the total EGRfraction to be achieved without closing intake or exhaust throttlevalves.
 11. A product as set forth in claim 2 wherein the target HP/LPEGR ratio is determined to optimize induction air temperature formaximum fuel economy.
 12. A product as set forth in claim 2 wherein thetarget HP/LP EGR ratio is determined to reduce exhaust emissions.
 13. Aproduct as set forth in claim 2 wherein the target HP/LP EGR ratio isachieved by open-loop control of an HP EGR valve opening or an LP EGRvalve opening to improve EGR response.
 14. A product as set forth inclaim 2 wherein the target HP/LP EGR ratio is determined to reducecompressor tip overheating.
 15. A product as set forth in claim 1,wherein the at least one other engine system input signal includes atleast one of turbocharger boost pressure or induction mass flow, and theoutput signals include at least one of HP EGR setpoints, LP EGRsetpoints, or turbocharger setpoints.
 16. A product as set forth inclaim 1, wherein the controller also includes HP and LP EGR controlmodules in communication with an induction control module to receive andprocess the output signals based on the target HP/LP EGR ratio andtransmit actuator command signals.
 17. A product as set forth in claim 2wherein the controller is also configured to estimate total EGR fractionresponsive to at least one sensed proxy parameter indicative of totalEGR fraction.
 18. A product as set forth in claim 17 wherein the atleast one sensed proxy parameter is cylinder pressure.
 19. A product asset forth in claim 1 wherein the estimated total EGR fraction isresponsive to at least one proxy parameter indicative of total EGRfraction and is input to at least one engine system model to generatethe estimated total EGR fraction.
 20. A product comprising: a controlsubsystem configured to: utilize at least one mass flow sensor tomeasured the mass flow of at least one gas in an induction plenum of anengine; use the measured mass flow as input to one or more systemmodels; estimate a target total EGR fraction responsive to the one ormore engine system models, and at least one other engine system inputsignal; send a signal representative of the target total EGR fraction toa controller configured to control exhaust gas recirculation (EGR)wherein the controller is also configured to: receive input signalsincluding the target total EGR fraction of an EGR system comprising atleast two EGR paths, determine a target HP/LP EGR ratio to control otherengine system parameters within the constraints of the target total EGRfraction, and transmit actuator output signals responsive to the targetHP/LP EGR ratio; wherein the controller is further configured to:generate HP EGR and LP EGR setpoints in accordance with the determinedtarget HP/LP EGR ratio, adjust at least one of the setpoints byprocessing an estimated total EGR fraction as process variable input andthe target total EGR fraction as setpoint input, and transmit thesetpoints as the actuator output signals to an EGR valve actuatorconfigured to move an EGR valve in response to the actuator outputsignal.